1. Field of the Invention
The present invention relates to a dielectric waveguide, particularly a dielectric waveguide for use in a transmission line or an integrated circuit for the millimeter-wave band or the micro-wave band.
2. Description of the Related Art
In a known dielectric waveguide, an electromagnetic wave is transferred along a dielectric strip provided between two parallel electrically conductive planes. Particularly when the distance between the two electrically conductive planes is set to half the wavelength or less to provide a non-propagating area, the known dielectric waveguide is a non-radiative dielectric waveguide ("NRD guide"), which does not radiate an electromagnetic wave from the dielectric strip. An NRD guide has been used as a transmission line having a low transmission loss or as an integrated dielectric waveguide apparatus.
FIGS. 15A and 15B are cross-sectional views showing two examples of conventional NRD guide configurations. In FIG. 15A, two metallic electrically conductive plates 12 form two parallel electrically conductive planes, and a dielectric strip 11 is disposed therebetween. FIG. 15B shows two dielectric plates 11' made from synthetic resin or dielectric ceramic and having dielectric strips 11 and electrode films 5 on the respective main surfaces of the dielectric plates 11'. The two dielectric plates 11' are disposed such that the dielectric strips 11 oppose each other. As described above, the NRD guides are formed with the dielectric strips serving as propagating areas and the areas on both sides thereof serving as non-propagating areas.
With the dielectric waveguide having the structure shown in FIG. 15A, the electrically conductive plates 12 and the dielectric strip 11 need to be manufactured separately, and it is difficult to position and secure the dielectric strip 11 against the electrically conductive plates 12. With the dielectric waveguide having the structure shown in FIG. 15B, to use the dielectric strips 11 as the propagating areas and the areas on both sides thereof as non-propagating areas, the side portions (flanges) of the dielectric plates 11' disposed in the non-propagating areas need to be thin. This brings about difficulty in manufacturing the dielectric waveguide and a strength problem may arise.